1. Field of the Invention
This invention relates to an improved apparatus for use in an offshore arctic environment. More particularly, this invention relates to an offshore structure located at or near the water surface and capable of housing equipment and even personnel wherein moving ice sheets floating along the surface of the water are deflected over the structure in a single mass.
2. Description of the Prior Art
There is a need in any offshore area where large moving ice sheets are encountered for a simple, inexpensive structure, capable of housing equipment and possibly even personnel and capable of withstanding the lateral loads due to the ice sheets striking the structure. Yet, the structure cannot be entirely submerged below the ice since access during ice free periods is required. Thus, the structure should be at or near the water surface.
Hudson et al, U.S. Pat. Nos. 3,972,199, (1976), Gerwick, 4,048,943, (1977), and Cranfield, J., "New Concept: Mobile Rig Design For Arctic Waters", Ocean Industry (March, 1976), pp. 77, 79 disclose several types of arctic caisson designs. However, these designs are fairly massive for the relatively simple task of housing equipment. Industry has long recognized the need for a simplified offshore arctic structure which is easy to fabricate and install in primarily shallow waters. However, design problems are encountered in developing a structure which is capable of withstanding the tremendous lateral loads associated with a striking ice sheet.
A specific example of the need for a simple, offshore structure capable of housing remotely operated equipment is found in a recovery technique for oil and gas. In the depletion of an oil reservoir it is occasionally necessary to inject large amounts of water into a producing well which extends from the ground surface into the reservoir. This secondary recovery procedure is termed waterflooding. The purpose of waterflooding is to displace the underground oil with the injected water thereby increasing the reservoir's productivity. As onshore oil production on the North Slope of Alaska increases, there is a need for large quantities of water to perform this waterflooding operation. Obviously, one of the preferred sources of water is the ocean since, typically, the onshore drilling site is relatively close to the shore line. However, pumping sea water onshore in the quantities desired for a waterflooding operation requires not only a large pipeline, i.e., 4-6 feet in diameter, but also a substantial amount of pumping equipment. The pumping equipment could be located offshore on a conventional floating or fixed structure. However, such offshore structures are very expensive and require a substantial lead time for their design and fabrication. Thus, while conventional arctic structures such as Hudson et al exhibit utility in supporting large drilling equipment, room for improvement remains in attempting to reduce the overall cost of such a structure while maintaining their ability to resist the large lateral loads.